U.S. patent number 6,732,051 [Application Number 09/839,466] was granted by the patent office on 2004-05-04 for seamless surveying system.
This patent grant is currently assigned to Trimble Navigation Limited. Invention is credited to Geoffrey R. Kirk, Darin Muncy, Joseph V. R. Paiva.
United States Patent |
6,732,051 |
Kirk , et al. |
May 4, 2004 |
Seamless surveying system
Abstract
A survey system and method for determining the best source of
position data for a particular application. The system includes
both an optical unit and a satellite positioning system (SATPS)
unit for obtaining position data. The optical unit includes a
theodolite and an electronic distance meter for determining the
position of a rover unit. The SATPS unit includes a SATPS antenna
and a SATPS receiver for receiving signals from satellites of the
SATPS and a radio for coupling the received signals to the rover
unit. The present invention automatically determines the best
source of position data. The best source of position data is then
used to calculate the position of the rover unit.
Inventors: |
Kirk; Geoffrey R. (San
Francisco, CA), Muncy; Darin (San Jose, CA), Paiva;
Joseph V. R. (Shawnee, KS) |
Assignee: |
Trimble Navigation Limited
(Sunnyvale, CA)
|
Family
ID: |
22649963 |
Appl.
No.: |
09/839,466 |
Filed: |
April 20, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
177780 |
Oct 22, 1998 |
6343254 |
|
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Current U.S.
Class: |
701/472;
342/357.52 |
Current CPC
Class: |
G01C
15/00 (20130101); G01S 19/48 (20130101) |
Current International
Class: |
G01C
15/00 (20060101); G01S 5/14 (20060101); G01C
021/26 (); G01S 005/14 () |
Field of
Search: |
;342/357.06,357.02,357.17 ;701/216 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Issing; Gregory C.
Attorney, Agent or Firm: Wagner Murabito & Hao LLP
Parent Case Text
This is a continuation of copending application(s) Ser. No.
09/177,780 filed on Oct. 22, 1998 now U.S. Pat. No. 6,343,254 which
is hereby incorporated by reference to this specification.
Claims
What is claimed is:
1. A seamless surveying system for use with a satellite positioning
system (SATPS) comprising: a first unit including a radio
transceiver and antenna, a first SATPS receiver, a first SATPS
antenna, said first unit being adapted to receive and transmit
SATPS data; a second unit including a radio transceiver and
antenna, a radiation source for irradiating a target with
transmitted radiation, a means for receiving reflected radiation
from said target, a means for determining the distance between said
target and said radiation source from said transmitted radiation
and said reflected radiation, and an instrument for determining
horizontal and vertical angles, and a second communication link;
and a third unit including a radio transceiver and antenna, a
target capable of reflecting said transmitted radiation, a third
communication link for communicating with said first unit and said
second unit, a second SATPS antenna, a second SATPS receiver, a
SATPS processor, and a logic unit for selecting an optimum data
source.
2. The system of claim 1 wherein said instrument is an
electro-optical instrument.
3. The system of claim 2 wherein said instrument comprises a
laser.
4. The system of claim 1 wherein said SATPS includes at least one
pseudolite.
5. The system of claim 1 wherein said instrument senses a magnetic
field.
6. The system of claim 1 wherein said logic unit is configured to
select the first source of position data that gives a position
within the desired accuracy range as the optimum data source.
7. The system of claim 1 wherein said logic unit is configured to
select said optimum data source on the basis of said distance
between said target and said radiation source.
8. A method for determining a position based upon data from an
optimum data source for a survey system that includes a first data
source for obtaining SATPS data, a second data source for obtaining
alternative data exclusive of SATPS data and a third unit adapted
to determine position, said method comprising: a) initiating a
position fix; b) receiving data at said third unit from ones of the
group consisting of said first data source and said second data
source; c) determining at said third unit the optimum data using
the data received in step b), and wherein the first received data
is designated to be the optimum data; and d) determining the
position of said third unit.
9. The method of claim 8 wherein said alternative data is obtained
in part by the use of an electro-optical device.
10. The method of claim 8 wherein said alternative data is obtained
in part by the use of an instrument for sensing a magnetic
field.
11. In a computer system including a processor coupled to a bus,
and a memory unit coupled to said bus for storing information, a
computer implemented method for determining the optimum data set
for a survey system which includes a first data source adapted to
receive SATPS data and a second data source adapted to receive
alternative data exclusive of SATPS data, said computer implemented
method comprising: a) initiating a position fix; b) receiving
position data from ones of said first data source and said second
data source; and d) determining the optimum data using said
position data received in step b), and wherein the first received
data is designated to be the optimum data for the determination of
the position.
12. The method of claim 11 wherein said SATPS data is in part
obtained from at least one pseudolite.
Description
TECHNICAL FIELD
This invention relates to systems and methods for determining
position. More specifically, the present invention relates to an
apparatus and method for determining the optimum source of data for
position determination when GPS data and optical data may be
available. The optimal source of position data is then used to
determine position.
BACKGROUND ART
Historically, surveying has been accomplished using optical
sighting methods. Optical sighting methods typically involve the
determination of distance, vertical angle and horizontal angle and
slope with reference to a known location at which a sighting device
is operated (reference site) by sighting to a remote location which
is positioned (the positioned site). Optical sighting methods
provide a high degree of accuracy as long as the distance between
the reference site and the staked site are short.
Recently, automated position determination systems have been used
for position determination in surveying applications. One such
system uses the constellation of Satellites in the Global
Positioning System (GPS) operated by the U.S. Air Force. The GPS
consists of a constellation of 24 orbiting satellites that transmit
signals via microwave radio. These signals may be used by
appropriately configured receivers to determine position.
One method for determining position uses the Coarse Acquisition
(C/A) code from four or more satellites to determine position. The
satellites mark their transmission digitally and the receiver
compares the time it receives the time mark with its own time
clock. The time delay, referred to as transit time, is typically in
the range of about 70-90 milliseconds. Pseudoranges are then
determined by multiplying transit time by the speed of radio
transmissions (approximately 300,000,000 meters/second). Position
is then determined using a geometric calculation that uses the
ephemerides and calculated pseudoranges. GPS based positions are
calculated using the World Geodetic System of 1984 (WGS84)
coordinate system. These positions are expressed in Earth Centered
Earth Fixed (ECEF) coordinates of X, Y, and Z axis. These positions
are often transformed into Latitude, Longitude, and Height relative
to the WGS84 ellipsoid.
Errors arise in the determined position due to timing/clock errors,
intentional introduction of error by the U.S. Air Force (referred
to hereinafter as "selective availability" or "S/A") and errors due
to atmospheric conditions. Atmospheric models can be used to
partially correct for errors due to atmospheric conditions.
However, because such corrections are inaccurate, they result in a
determination of position that is not highly accurate.
For surveying applications a high degree of accuracy is required in
determining position. Therefore, a position determination technique
which provides the necessary accuracy by correcting for S/A, and
correcting for atmospheric conditions is typically used. One such
method is real time kinematic (RTK) position determination.
RTK systems typically include a reference GPS receiver and a roving
GPS receiver. The reference GPS receiver receives signals from GPS
satellites. Then, either correction data or raw observables data is
transmitted to a roving GPS receiver. The roving GPS receiver also
receives signals from GPS satellites. The signals received by the
roving GPS receiver and the data from the reference GPS receiver
are then used to determine the position of the roving GPS receiver
with a high degree of accuracy. Typically carrier phase
measurements are used to determine position in RTK systems. RTK
systems provide a high degree of accuracy provided that the
differential separation distance between the reference GPS receiver
and the roving GPS receiver is within a predetermined range.
However, at very short distances, optical methods are more accurate
than RTK methods.
Optical systems are often undesirable for use in a particular
survey due to obstructions and terrain contours that prevent direct
visual observation of a remote location to be positioned. When
obstructions prevent optical measurements or when the distances are
so great that optical measurements do not provide the required
accuracy, RTK systems are often used.
However, either an optical system or a GPS system alone is usually
used to survey a particular location. This requires an advance
determination as to which system is to be used each time a survey
is to be taken. This process is time consuming and requires an
in-depth knowledge of the capabilities and limitations of each
system. Also, an in-depth knowledge of the location to be surveyed
is required.
What is needed is an apparatus and method for surveying that
incorporates the advantages of both optical systems and GPS
systems. In addition, a method for accurately determining position
is needed that uses both optical measurements and GPS measurements.
Furthermore, a surveying system that is easy to use and operate is
required.
DISCLOSURE OF THE INVENTION
The present invention provides a system that swiftly and
automatically determines which type of data will provide the best
survey of a particular site. The best source of position data is
then used to determine the desired position.
In one embodiment of the present invention, the seamless surveying
system includes a Satellite Positioning System (SATPS) unit, an
optical unit and a rover unit. In one embodiment, SATPS signals
from satellites of the US Global Positioning System (GPS) are
received at the SATPS unit and are coupled to the rover unit. The
rover unit includes a target that is adapted to be engaged by the
optical unit for optically determining the position of the rover
unit. The rover unit includes logic for determining the optimum
source of positioning data to be used for determining position.
When the seamless surveying system includes a SATPS unit and an
optical unit, the rover unit determines whether optical data from
the optical unit or SATPS data from the SATPS unit are to be used
for determining position.
In one embodiment, the optimum source of position data is chosen
based on time. That is, the first received source of position data
is determined to be the optimum source of position data. The
optimum source of position data is then used to determine position.
Thus, when optical data is received first, optical data is used to
determine position. Similarly, when SATPS data is received first,
SATPS data is used to determine position. This allows for the
fastest computation of position.
In another embodiment, the optimum source of position data is
chosen based on the distance between the rover unit and the optical
system. That is, because optical data give good results at short
distances, if both optical data and SATPS data are available, and
if the distance is less than a predetermined threshold (the optical
threshold), optical data is used. Since SATPS data gives good
results at longer distances, SATPS data is used when the distance
is greater than or equal to the optical threshold.
In another embodiment, a weighting process is used to determine the
optimum source of position data.
In yet another embodiment, the measurements from both the optical
unit and the SATPS unit are combined to determine position.
The seamless surveying system of the present invention monitors
multiple sources of position data and selects from the available
sources of position data the optimum source of position data for a
particular application. Therefore, there is no need for the user to
determine which type of system to use as is required with prior art
systems. Because the determination is automatic, there is no need
for human intervention for changing from one system to another. In
addition, the seamless surveying system of the present invention is
easy to use since data from the optimum source of position data is
automatically coupled to the rover unit and is used for accurate
determination of position.
These and other objects and advantages of the present invention
will no doubt become obvious to those of ordinary skill in the art
after having read the following detailed description of the
preferred embodiments which are illustrated in the various drawing
figures.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and form a
part of this specification, illustrate embodiments of the invention
and, together with the description, serve to explain the principles
of the invention:
FIG. 1 is a schematic diagram of a seamless surveying system that
is receiving signals from satellites of a SATPS in accordance with
the present invention.
FIG. 2 is a flow chart illustrating a method for determining
position that uses the optimum source of position data in
accordance with the present claimed invention.
FIG. 3 is a diagram of a rover unit in accordance with the present
claimed invention.
FIG. 4 is a diagram of an optical unit in accordance with the
present claimed invention.
FIG. 5A is a diagram of a SATPS base unit in accordance with the
present claimed invention.
FIG. 5B is a diagram of an integrated base unit that performs the
functions of a SATPS base unit and an optical unit in accordance
with the present claimed invention.
FIG. 6 is a schematic diagram illustrating an exemplary computer
system used as part of a seamless survey system in accordance with
the present claimed invention.
FIG. 7 is a flow chart illustrating a method for determining the
optimum source of position data that uses separation distance in
accordance with the present claimed invention.
FIG. 8 is a flow chart illustrating a method for determining the
optimum source of position data that uses a precision threshold in
accordance with the present claimed invention.
FIG. 9 is a chart showing an example of weighting variables and
weighting factors used to determine the optimum source of position
data in accordance with the present claimed invention.
FIG. 10 is a flow chart illustrating a method for accurately
determining position in accordance with the present claimed
invention.
FIG. 11 is a perspective view of one embodiment of the components
used for the reference station and mobile station according to the
invention.
FIG. 12 is a schematic view of a retro-reflector used at the mobile
station or the reference station according to one embodiment of the
invention.
FIGS. 13A and 13B together provide a schematic view of a signal
processing system used for the reference station and for the mobile
station according to one embodiment of the invention.
FIGS. 14A and 14B are front and back perspective views of a
conventional electro-optical instrument that determines the
horizontal bearing, vertical angle and length of a vector joining
this instrument with a second instrument that responds to receipt
of an electromagnetic wave from the first instrument by returning a
signal to the first instrument.
FIG. 15 illustrates how phase integer ambiguities occur in an
SATPS.
FIGS. 16 and 17 illustrate reductions in search volume for the
correct carrier phase integers that are available with the
invention in two approaches.
BEST MODE FOR CARRYING OUT THE INVENTION
Reference will now be made in detail to the preferred embodiments
of the invention, examples of which are illustrated in the
accompanying drawings. While the invention will be described in
conjunction with the preferred embodiments, it will be understood
that they are not intended to limit the invention to these
embodiments. On the contrary, the invention is intended to cover
alternatives, modifications and equivalents, which may be included
within the spirit and scope of the invention as defined by the
appended claims. Furthermore, in the following detailed description
of the present invention, numerous specific details are set forth
in order to provide a thorough understanding of the present
invention. However, it will be obvious to one of ordinary skill in
the art that the present invention may be practiced without these
specific details. In other instances, well known methods,
procedures, components, and circuits have not been described in
detail as not to unnecessarily obscure aspects of the present
invention.
Some portions of the detailed descriptions that follow are
presented in terms of procedures, logic blocks, processing, and
other symbolic representations of operations on data bits within a
computer memory. These descriptions and representations are the
means used by those skilled in the data processing arts to most
effectively convey the substance of their work to others skilled in
the art. In the present application, a procedure, logic block,
process, etc., is conceived to be a self-consistent sequence of
steps or instructions leading to a desired result. The steps are
those requiring physical manipulations of physical quantities.
Usually, though not necessarily, these quantities take the form of
electrical or magnetic signals capable of being stored,
transferred, combined, compared, and otherwise manipulated in a
computer system. It has proven convenient at times, principally for
reasons of common usage, to refer to these signals as bits, values,
elements, symbols, characters, terms, numbers, or the like.
It should be borne in mind, however, that all of these and similar
terms are to be associated with the appropriate physical quantities
and are merely convenient labels applied to these quantities.
Unless specifically stated otherwise as apparent from the following
discussions, it is appreciated that throughout the present
invention, discussions utilizing terms such as "designating",
"incorporating", "calculating", "determining", "communicating" or
the like, refer to the actions and processes of a computer system,
or similar electronic computing device. The computer system or
similar electronic computing device manipulates and transforms data
represented as physical (electronic) quantities within the computer
system's registers and memories into other data similarly
represented as physical quantities within the computer system
memories or registers or other such information storage,
transmission, or display devices.
Although the methods and apparatus of the present invention are
described with reference to the use of a Satellite Positioning
System (SATPS) for determining position, it will be appreciated
that the teachings are equally applicable to positioning systems
that utilize pseudolites or a combination of pseudolites and
satellites. Pseudolites are ground-based transmitters that
broadcast a Pseudo Random Noise (PRN) code (similar to a SATPS
signal) modulated on an L-band carrier signal, generally
synchronized with SATPS time. Typically, each transmitter is
assigned a unique PRN code so as to permit identification by a
remote receiver. The term "SATPS", as used herein, is intended to
include pseudolite or equivalents of pseudolites, and the term
"SATPS signals" and "SATPS data", as used herein, is intended to
include SATPS-like signals and data from pseudolites or equivalents
of pseudolites.
In one embodiment, the SATPS uses satellites of the U.S. Global
Positioning System (GPS). However, the methods and apparatus of the
present invention are equally applicable for use with other
satellite-based positioning systems such as, for example the
GLONASS system. The GLONASS system includes satellites that emit
signals at slightly different carrier frequencies, with individual
satellites identified by the frequency of transmission.
Alternatively, signals from other sources such as LORAN, Wide Area
Augmentation System (WAAS) satellites, etc. may be used to
determine position.
Referring now to FIG. 1, a number of satellites, shown generally as
satellites 6 associated with the SATPS transmit their positions in
a broadcast mode to all points within their respective fields of
view on the earth's surface. Reference stations can determine their
positions using the SATPS data directly received from satellites 6
("uncorrected SATPS data"). Signals received directly from
satellites are corrupted by a number of error sources such as, for
example, Selective Availability, ephemeris prediction errors,
timing errors, and errors in the estimation of ionospheric and
tropospheric delay.
Continuing with FIG. 1, in the present invention, a reference
station such as SATPS base unit 1 that receives uncorrected SATPS
data from satellites 6 and retransmits the uncorrected SATPS data
as shown by arrow 4. The transmitted uncorrected SATPS data from
SATPS base unit 4 is used by other SATPS receivers such as rover
unit 2 to accurately determine position. Methods for determining
position using multiple SATPS receivers are well known in the art
and include RTK methods that use carrier signals to accurately
determine position. However, other methods such as "differential"
correction methods may also be used to determine the position of
rover unit 2.
Still referring to FIG. 1, in addition to SATPS base unit 4 and
rover unit 2, seamless surveying system 100 also includes an
optical system such as optical unit 3. Optical unit 3 includes an
optical system capable of determining the position of a target. In
one embodiment, rover unit 2 communicates with optical unit 3 via a
communication link as shown by arrow 5 to indicate that position is
to be determined. Optical unit 3 then determines the position of
rover unit 2 relative to optical unit 3. Optical data from optical
unit 3 is then coupled to rover unit 2.
Referring now to FIG. 2, a method for determining position using
the optimum source of position data is shown. When a user desires
to determine position, the user initiates the position fix as shown
by step 20. That is, the user takes some action to start the
position determination process.
Referring to FIG. 3, an embodiment of a rover unit is shown. In
this embodiment, rover unit 2 includes an input device 35 that is
used to initiate the position fix. In one embodiment input device
35 is a keypad which includes a standard keypad. Alternatively,
input device 35 may consist of a touch screen or dedicated function
keys. When input device 35 includes dedicated function keys, a
position fix is initiated by operating a dedicated function
key.
Referring back to FIG. 2, position data is received (step 21) from
SATPS sources such as SATPS base unit 1 (FIG. 1) and optical
sources such as optical unit 3. The optimum source of position data
is then determined as shown by step 22. In one embodiment, the
first source of position data to be received is determined to be
the optimum source of position data. This allows for the fastest
possible determination of position.
In the embodiment shown in FIG. 3, rover unit 2 receives position
data via communication link 31. Communication link 31 includes a
radio unit antenna 33 and a radio transceiver 32. The received
position data can include SATPS data from a SATPS receiver such as
SATPS base unit 1 of FIG. 1 and optical data from an optical system
such as optical unit 3.
Referring back to FIG. 2, the determined optimum source of position
data is then used to determine position as shown by step 23. When
SATPS data is used to determine position, position is determined
using any of a number of known methods. In one embodiment, position
is determined using RTK methods that use carrier signals to
accurately determine position.
FIG. 4 shows an embodiment of optical unit 3 that includes input
device 43. In one embodiment, optical unit 3 is placed at a known
position and the position of optical unit 3 is manually input using
input device 43. Input device 43 may be a standard alphanumeric
keypad, or other device for data input. Alternatively, input device
43 is a numeric keypad, a touch screen or dedicated function keys
operable in conjunction with a display (not shown).
Upon initiation of a position fix, rover unit 2 communicates with
optical unit 3 via communication link 41 of FIG. 4. Communication
link 41 includes radio antenna 33 and radio transceiver 32. Upon
receiving a signal indicating initiation of a position fix, optical
system 42 determines the position of rover unit 2 (FIGS. 1 and 3).
This may be done using any of a number of known optical sighting
methods. In one embodiment, optical system 42 includes an
electronic distance meter (EDM) 44 and a theodolite 45. EDM 44
transmits electromagnetic waves having wavelengths that lie in the
near-infrared, infrared, visible or ultraviolet range that are used
for determining distance. Theodolite 45 determines horizontal and
vertical angles.
In one embodiment, optical target 34 of FIG. 3 is an optical target
designed to reflect electromagnetic waves from optical system 42.
That is, when EDM 44 transmits electromagnetic waves, optical
target 34 of FIG. 3 is a target adapted to reflect electromagnetic
waves back toward optical system 42. In one embodiment, optical
target 34 of FIG. 3 is an array of antenna components that receive
electromagnetic waves and retransmit the received electromagnetic
waves at a microwave or infrared frequency. By analysis of the
return radiation and the angles measured by theodolite 45, optical
system 42 determines the position of rover unit 2. This position is
then communicated to rover unit 2 via communication link 41 of FIG.
4. A system for determining position using an EDM and a theodolite
is described in U.S. Pat. No. 5,471,218 which is incorporated in
part in the following section.
REFERENCED ART
(U.S. Pat. No. 5,471,128)
FIELD OF THE INVENTION
This invention relates to surveying and to the use of Satellite
Positioning System information to improve the accuracy and
productivity of such surveying.
BACKGROUND OF THE INVENTION
As noted by A. Bannister and S. Raymond in Surveying, Pitman
Publishing Ltd., London, 1977, general method of surveying was
known and practiced more than 2000 years ago. The methods used at
that time were simple but subject to consistency errors and
required considerable time to perform. Surveying instruments have
improved considerably since about 1900, taking advantage of
advances in electronics, optics and other related disciplines.
Recently, lasers, electro-optics, wave interaction and phase
detection have been introduced into, and used in, surveying
activities.
Use of a laser beam projector for surveying operations is disclosed
in U.S. Pat. No. 3,471,234, issued to Studebaker. The beam rotates
over terrain to be surveyed, and a beam point may be directed to a
particular location and used to measure elevation and angular
displacements within the region covered by the rotating beam.
Altman, in U.S. Pat. No. 3,669,548, discloses a method for
determining a ship's heading or bearing, using an electro-optical
angle measuring device that determines angles relative to a
horizontal datum line. A plurality of parallel light beams, spaced
apart by known, uniform distances and oriented at a. known angle,
forms a one-dimensional grid that covers the region where the ship
is located. A rotating reflecting telescope on the ship has its
axis aligned with one of the parallel light beams. The angle of the
ship's longitudinal axis relative to the known direction of the
parallel light beams is then easily read off to determine the
ship's heading. This approach would not be suitable where the ship
or other body whose angular orientation is to be determined can
move over a large region.
Remote measurement of rotation angle of an object of interest by
use of polarized light and electro-optical sensors is disclosed by
Weiss et al in U.S. Pat. No. 3,877,816. The intensity of light
transmitted serially through two linear polarization filters is
proportional to the square of the cosine of the angle between the
two polarization directions, and the proportionality constant can
be determined by experiment. Unpolarized light transmitted along a
first reference path with fixed polarization directions is compared
with unpolarized light transmitted along a second, spatially
separated and optically baffled path in which the polarization
direction of one polarizer may vary. One or two light polarizers in
each light beam path rotates at a constant angular velocity, which
is the same for each path, and the difference in phase of the two
received light signals is a measure of the angle of rotation of a
polarizer (or the body to which the polarizer is attached) in the
first path and a polarizer in the second path.
An optical-electronic surveying system that also determines and
displays the angular orientation of a survey pole relative to a
local horizontal plane is disclosed in U.S. Pat. No. 4,146,927,
issued to Erickson et al. The system can receive and process range
measurements directly from an electronic distance meter located
near the system.
U.S. Pat. No. 4,443,103, issued to Erdmann et al, discloses use of
a retro-reflective, electro-optical angle measuring system, to
provide angle measurements after interruption of a signal that
initially provided such information. A light beam is split into two
beams, which intersect on a scanning mirror, which rotates or
vibrates about a fixed axis, and the two beams are received at
different locations on a retro-reflective tape positioned on a flat
target surface on the target whose rotation is to bemeasured. These
two beams form a plane that moves as the scanning mirror moves,
with a reference plane being defined by the mirror at rest in a
selected position. The scanning mirror sweeps the plane of the two
beams across the target surface. A rotation angle of the target
surface relative to the reference plane is determined, based upon
the time difference between receipt of light from each of the two
retro-reflected beams. The beam interception times coincide only if
an edge of the retro-reflective tape is parallel to the reference
plane. If receipt of light from the two retro-reflected beams is
displayed on a synchronized, two-trace oscilloscope screen, the two
"blips" corresponding to receipt of these two beams will have a
visually distinguishable and measurable time difference .DELTA.t,
as indicated in FIGS. 2A, 2B and 2C of the Erdmann et al patent.
The time difference .DELTA.t will vary as the scanning mirror
moves. A second Erdmann et al patent, U.S. Pat. No. 4,492,465,
discloses a similar approach but with different claims.
"Total station" electronic instrumentation for surveying, and more
particularly for measurement of elevation differences, is disclosed
by Wells et al in U.S. Pat. No. 4,717,251. A rotatable wedge is
positioned along a surveying transit line-of-sight, which is
arranged to be parallel to a local horizontal plane. As the wedge
is rotated, the line-of-sight is increasingly diverted until the
line-of-sight passes through a target. The angular displacement is
then determined by electro-optical encoder means, and the elevation
difference is determined from the distance to the target and the
angular displacement. This device can be used to align a
line-of-sight from one survey transit with another survey transit
or to a retro-reflector. However, the angular displacement is
limited to a small angular sweep, such as 12.degree..
Fodale et al disclose an electro-optical spin measurement system
for use in a scale model airplane wind tunnel in U.S. Pat. No.
4,932,777. Optical targets (six) to receive and sense one or
several light beams are located under the fuselage at the nose tip,
on each of two sides of the fuselage, and under each wing tip, and
a plurality of optical receivers are positioned on the perimeter of
the wind tunnel to receive light from the optical targets at
various angles, to determine airplane angle of attack and roll
angle. The time-synchronized signals received at each receiver are:
recorded for subsequent analysis.
In U.S. Pat. No. 4,954,833, issued to Evans et al, information on
deflection of the local vertical (obtained from gravity
measurements) is combined with geodetic azimuth estimated from GPS
signals to obtain an astronomical azimuth. This azimuth can be used
for ballistic projectile delivery to a selected target. This method
does not focus on integration of GPS operation with theodolite
operation but, rather, seeks to avoid use of a theodolite to obtain
the astronomical azimuth.
Kroupa et al, in U.S. Pat. No. 4,988,189, disclose use of a passive
rangefinding system in combination with an electro-optical system,
using image information obtained at two or more electro-optical
system positions.
A method for simultaneously measuring the difference between
orthometric (geoidal) height and height above a given ellipsoid for
a site on the Earth's surface is disclosed by Evans in U.S. Pat.
No. 5,030,957. Two or more leveling rods are held at fixed, spaced
apart locations, with a known baseline vector between the rods.
Each levelling rod holds a GPS signal antenna, receiver and
processor that determines a GPS location for each rod. The
geometric height of the GPS antenna (or of the intersection of the
rod with the Earth's surface) is determined for each rod, and the
geometric height difference is determined, using standard GPS
survey measurements (accurate to within a few centimeters). A
comparison of the orthometric height, usually found using a spirit
level, and the height above the ellipsoid, obtained from a GPS
measurement, provides a measure of the local gravitational field.
The patent does not indicate, or perhaps recognize, advantages of
use of height information to aid the GPS carrier phase
initialization process but treats the GPS and the levelling rods as
separate, non-interacting systems.
Ohishi et al disclose an optical distance measuring instrument
using light transmitted and returned by retro-reflection in U.S.
Pat. No. 5,054,911. A light beam pulse generated at the instrument
is split into two pulses; one pulse is immediately received by a
laser diode as a reference pulse. The other pulse is transmitted to
a retro-reflector at a remote or adjacent target and returned to
the instrument by retro-reflection thereat. The returning pulse is
received by an optical fiber, having a known time delay .DELTA.t
and then received by the laser diode to provide a second pulse. The
time delay .DELTA.t is subtracted from the difference of arrival
times of the two pulses and divided by 2c (c=ambient medium light
velocity) to obtain the distance from instrument to target.
A somewhat unclear disclosure of a beam alignment apparatus and
method is presented in U.S. Pat. No. 5,060,304, issued to Solinsky.
Two substantially identical beam acquisition apparati are spaced
apart from each other, each apparatus including two identical
parabolic mirrors with parallel axes, each mirror having an axial
aperture through which an electromagnetic wave beam passes and
having a second smaller mirror located at the parabola's focal
point. Each parabolic mirror has a third mirror consisting of a
plurality of small retro-reflectors, located adjacent to but behind
the parabolic mirror so that the parabolic mirror lies between the
second and third mirrors. One parabolic mirror in each pair
receives light from a transmitter positioned behind the mirror
aperture and transmits this beam in a direction parallel to the
mirror axis. The other parabolic mirror in each pair receives an
incident beam propagating parallel to its axis and reflects this
light to a receiver located behind the mirror aperture. One of the
parabolic mirror pairs is operated in a search mode (moving) at a
first selected frequency f1. The second parabolic mirror pair is
operated in a "stare" mode at a selected frequency f2.noteq.f1. As
the two mirror pairs come close to alignment with each other, the
mirror pairs sense this by receipt of a retro-reflected beam or a
directly transmitted beam, the distinction being made by the
frequency of the beam received. The search mode mirror pair, and
then the stare mode mirror pair, can then be brought into alignment
with each other.
A surveying instrument that uses GPS measurements for determining
location of a terrestrial site that is not necessarily within a
line-of-sight of the surveyor is disclosed in U.S. Pat. No.
5,077,557 issued to Ingensand. The instrument uses a GPS signal
antenna, receiver and processor, combined with a conventional
electro-optical or ultrasonic range finder and a local magnetic
field vector sensor, at the surveyor's location. The range finder
is used to determine the distance to a selected mark that is
provided with a signal reflector to return a signal issued by the
range finder to the range finder. The magnetic field vector sensor
is apparently used to help determine the surveyor's location and to
determine the angle of inclination from the surveyor's location to
the selected mark.
U.S. Pat. No. 5,101,356, issued to Timothy et al, discloses a
moving vehicle attitude measuring system that mounts three GPS
signal antennas in a non-collinear configuration on the vehicle at
predetermined distances from each other. Each antenna is connected
to a GPS receiver/processor. The phases of rf signals arriving at
the antennas are compared to determine the angular orientation of
the plane containing the three antennas, and the angular
orientation of the vehicle that carries these antennas.
Method and apparatus for measuring the relative displacement of two
objects, applicable to monitoring of movement of adjacent material
along an earthquake fault, is disclosed in U.S. Pat. No. 5,112,130,
issued to Isawa. First and second optical distance measuring
instruments (ODMIs) are placed at known locations astride a
selected line (e.g., a fault line). First and second optical
reflectors, also astride the selected line, are spaced apart by
known distances from the first and second ODMIs. Distances from the
first ODMI to the second reflector and from the second ODMI to the
first reflector are measured ab initio and compared with subsequent
readings of these two distances. If one or both of these distances
changes, the magnitudes of the changes are used to determine how
far the Earth on one side of the line has moved relative to the
Earth on the other side of the line, as might occur in a slip along
a fault line.
Ghaem et al disclose an electronic direction finder that avoids
reliance on sensing of terrestrial magnetic fields for establishing
a preferred direction for satellite signal acquisition in U.S. Pat.
No. 5,146,231. The apparatus uses a receiver/processor for GPS or
similar navigation signals received from a satellite, and requires
(stored) knowledge of the present location of at least one
reference satellite from which signals are received. The
orientation of the finder or its housing relative to a line of
sight vector from the finder to this reference satellite is
determined. This orientation is visually displayed as a projection
on a horizontal plane. Any other direction in this horizontal plane
can then be determined with reference to this projection from a
knowledge of the reference satellite location.
U.S. Pat. No. 5,142,400, issued to Solinsky, discloses a method for
line-of-sight acquisition of two optical beam transceivers suitable
for use in satellite communications. A first beam transceiver has
an optical retro-reflector and initially operates in a passive or
"stare" mode, with its beam transmitted in a fixed direction. A
second transceiver performs a search over 2.pi. steradians with its
optical beam until it receives, from the first transceiver, either
(1) a return of its own beam or (2) a distinguishable beam from the
first transceiver. Boresight alignment is then maintained after
beam-to-beam acquisition.
U.S. Pat. No. 5,146,290, issued to Hartrumpf, discloses apparatus
for determining the position and angular orientation of an object.
A partially silvered hemispherical light reflector is fixed to some
part of the object, and two spaced apart laser beams are directed
to intersect at the hemisphere center, to be (partly)
retro-reflected at the hemisphere reflector surface, and to return
toward the laser sources, to be detected by photodetectors located
adjacent to each laser source. A portion of the beam from each
laser source is transmitted through the hemispherical reflector and
is received by a line or plane of photodetectors positioned on a
plane behind the hemispherical reflector. As the object is
translated or rotated, the locations where the reflected and
transmitted beams are received by the photodetector arrays changes
in a manner that can be related to the translation and/or rotation
of the object.
A theodolite and tape have traditionally been used to measure
horizontal and vertical angles and distances in terrestrial
surveying. Recently, digital theodolites, as described in U.S. Pat.
No. 3,768,911, issued to Erickson, and electronic distance meters
(EDMs), as described by Hines et al in U.S. Pat. No. 3,778,159,
have supplanted the theodolite and tape approach. Combination of an
optical angle encoder and an EDM in an integrated package (called
an "electronic total station"), as disclosed in U.S. Pat. No.
4,146,927, issued to Erickson et al, has led to automation of field
procedures, plan production and design work.
Several limitations exist in use of a conventional total station.
First, it is difficult to quickly establish the angular orientation
and absolute location of a local survey or datum. Many surveys are
not related to a uniform datum but exist only on a localized datum.
In order to accurately orient a survey to a global reference, such
as astronomical north, a star observation for azimuth is often used
that requires long and complicated field procedures. Second, if a
survey is to be connected to a national or state geodetic datum,
the survey sometimes must be extended long distances, such as tens
of kilometers, depending upon the proximity of the survey to
geodetic control marks. Third, the electronic total station relies
upon line-of-sight contact between the survey instrument and the
rodman or pole carrier, which can be a problem in undulating
terrains.
These systems do not provide the benefits of an integrated SATPS
and terrestrial total station instrument. What is needed is a
system that provides: (1) rapid azimuth and location determination
in a fixed reference frame; (2) prompt resolution of the carrier
phase ambiguities that occur in a SATPS; (3) distance and angle
information without requiring line-of-sight contact between a
reference station and a mobile station; (4) fail-safe capability
for crosschecking, and calibrating the respective error sources in,
the location information provided by the SATPS and by the
terrestrial positioning system; and (5) capability for accounting
for height differences between the geoid and ellipsoid over the
local survey area.
SUMMARY OF THE INVENTION
These needs are met by the invention, which provides a surveying
system that combines Satellite Positioning System (SATPS)
techniques with new and with known survey techniques. The apparatus
includes a first or reference station that provides a reference for
the survey and whose location is determined with high accuracy, and
a second or mobile station that is spaced apart from the first
station and acts as a mobile measurement unit for the survey. More
than one mobile station can be used simultaneously with one
reference station. The reference station includes a first Satellite
Positioning System (SATPS) antenna and first SATPS
receiver/processor, connected together, for receiving SATPS signals
from two or more SATPS satellites and for determining the location
of the reference station according to the SATPS signals. The first
SATPS receiver/processor is adapted for determining the difference,
if any, between the location, known with high accuracy, of the
reference station and the location of the reference station as
determined by the SATPS satellite signals. The reference station
also includes a reference station communications antenna, connected
to the first SATPS receiver/processor, for transmitting or
receiving station location and point attribute information. The
reference station also includes an electronic distance meter (EDM)
and digital theodolite, whose spatial orientation can be varied
arbitrarily, connected to the first SATPS receiver/processor, for
transmitting electromagnetic waves having a selected wavelength and
for determining the distance from the reference station to the
mobile station by receipt of a return electromagnetic signal from
the mobile station, for determining the elevation difference, if
any, between the reference station and the mobile station, and for
determining the angular displacement between a line drawn between
the reference station and the mobile station and a selected
reference line.
The mobile station includes a second Satellite Positioning System
(SATPS) antenna and second SATPS receiver/processor, connected
together, for receiving SATPS signals from two or more SATPS
satellites and for determining the location of the mobile station
according to the SATPS signals. A second station communications
antenna, connected to the second SATPS receiver/processor, for
communicating with the reference station communications antenna and
for transmitting to the reference station a signal containing
feature and attribute information and information on the location
of the mobile station as determined by the SATPS satellite signals,
is also included in the mobile station. The mobile station also
includes an electronic distance meter responder, adapted to receive
the electromagnetic waves transmitted by the electronic distance
meter and to provide a return electromagnetic signal that is
received by the electronic distance meter at the reference station.
The reference station communication means and the mobile station
communication means are connected by a data link for transferring
information from one station to the other station.
The invention provides a "total SATPS station", including first and
second spaced apart SATPS station; whose relative separation is
determined with high accuracy, as a supplement to survey equipment.
Each of the first and second SATPS stations includes an SATPS
antenna and SATPS receiver/processor that receive signals from two
or more SATPS satellites and process these signals to partly or
fully determine the position of the SATPS antenna. The first and
second SATPS antenna and associated SATPS receiver/processor may be
retrofitted within first and second housings, respectively, that
contain conventional first and second electro-optical survey
instruments, respectively, used to determine the beating, length
of, and/or height difference of a separation vector joining the two
electro-optical survey instruments.
The invention uses certain electro-optical survey measurements,
implemented by use of one or more: signal retro-reflectors that
operate in the microwave, infrared, visible or ultraviolet
wavelength ranges, to determine the bearing, length of, and/or
height difference of a separation vector joining the first and
second stations. This requires that the two stations have
line-of-sight visual contact. The primary object is to implement
carder phase positioning (accurate to within a few centimeters), or
the less accurate code phase positioning, using the SATPS satellite
signals. Carrier phase positioning is implemented by causing two or
more SATPS stations track a common group of SATPS satellites. The
measurements are then merged and either processed in real time, or
postprocessed, to obtain data useful in determination of the
location of any stationary or mobile SATPS station adjacent to an
SATPS reference station. Real time positioning requires transfer of
SATPS data between a reference station and a mobile station, using
a data link that need not rely upon line-of-sight
communication.
One problem that must be overcome initially in use of carrier phase
positioning is the presence of phase integer ambiguities in the
carrier phase measurements for the tracked satellites. An integer
search technique for identification of the phase integers often
takes account of the statistical nature of discrete integer
combinations that are realistic candidates for the proper phase
integers. The number of possible combinations to be searched is
enormous, unless the number of candidates can be reduced ab initio.
If the relative location of two SATPS stations is known precisely,
the number of initial phase integer combination candidates can be
reduced to as few as one. If the horizontal or vertical separation
distance between the two stations is known with high accuracy in
the SATPS frame, the number of phase integer combination candidates
can be reduced to a modest number that can be searched relatively
quickly and can reliably produce the correct results. The number of
phase integer combination candidates is reduced by sequentially
applying position information provided by the electro-optical
survey measurements
Another serious problem with carrier phase positioning is the
possibility of SATPS signal interruptions at one or both SATPS
stations. When a SATPS satellite signal is lost, the phase
integer(s) must be redetermined. Signal interruption can easily
occur in urban or other built-up areas where tall structures
interfere with or produce multipath SATPS signals. A separation
vector between two SATPS stations, specified by three coordinate
differences, or by a vector magnitude and two or more spherical
angles relative to a fixed direction, may be known initially.
However, one or both of these stations may have moved when the
signal is interrupted so that the separation vector must be
established again.
The invention provides a separation vector, between the two
stations by use of one or more wave retro-directors that are
mounted on the second station and facing the first station. An
electromagnetic wave beam ("light beam") is directed from the first
station toward the second station, and the beam is retro-reflected
from the second station toward the first station. The
station-to-station separation vector is obtained by electro-optical
phase measurement techniques. Once the separation vector is
re-established, after an SATPS signal interruption occurs, the
phase integer combination for the two station is promptly
redetermined, and static or kinematic surveying can continue.
Several benefits accrue from this total station approach: (1) rapid
azimuthal angle determinations can be made; (2) use of differential
SATPS information supplements and improves the accuracy of the
survey parameters that can be measured; (3) SATPS signal processing
can be done at the reference station or at the mobile station; (4)
where the frequency of the station-to-station data link is selected
appropriately, or where one or more signal repeaters are used to
relay signals between the two stations, survey measurements are not
limited to line-of-sight measurements from reference station to a
mobile station, once the phase integer ambiguities are resolved;
and (5) systematic and random errors in the SATPS and
electro-optical measurements can be determined and reduced by
combining the information from the two systems.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 11 is a perspective view of one embodiment of the components
used for the reference station and mobile station according to the
invention.
FIG. 12 is a schematic view of a retro-reflector used at the mobile
station or the reference station according to one embodiment of the
invention.
FIGS. 13A and 13B together provide a schematic view of a signal
processing system used for the reference station and for the mobile
station according to one embodiment of the invention.
FIGS. 14A and 14B are front and back perspective views of a
conventional electro-optical instrument that determines the
horizontal bearing, vertical angle and length of a vector joining
this instrument with a second instrument that responds to receipt
of an electromagnetic wave from the first instrument by returning a
signal to the first instrument.
FIG. 15 illustrates how phase integer ambiguities occur in an
SATPS.
FIGS. 16 and 17 illustrate reductions in search volume for the
correct carrier phase integers that are available with the
invention in two approaches.
DESCRIPTION OF BEST MODE OF THE INVENTION
FIG. 11 illustrates many of the components included in a reference
station 1111 and a mobile station 1131 according to one embodiment
of the invention. The reference station 1111 includes a plate 1113
mounted on a tripod or other stable structure (not shown) and
rotatable about an approximately vertical first axis AA that passes
through the plate 1113. A second body 1115, referred to as the
alidade, is mounted on a top surface of the plate 1113 and is
either rotatable about the first axis AA with respect to the plate
1113 or rotates with the plate 1113 about the first axis AA. A
third body 1117 is positioned adjacent to or surrounded by the
alidade 1115 and rotates about an approximately horizontal second
axis BB, referred to as the trunnion or horizontal axis, with
respect to the alidade 1115. The third body 1117 includes an EDM
1119 that may be aimed or pointed in an arbitrary direction (over a
hemisphere with included solid angle approximately 2.pi.
steradians) with the aid of rotations of the first, second and
third bodies about the first and second axes AA and BB. In one
embodiment, the EDM 1119 relies upon electro-optical principles and
emits electromagnetic waves W with a fixed wavelength .lambda. that
is known to high accuracy. The waves W are reflected at, or
otherwise interact with, the mobile station 1131, and a return
signal from the mobile station is used to determine the distance
from the reference station 1111 to the mobile station 1131.
The reference station 1111 determines the horizontal or azimuthal
angle .theta..sub.h of a reference station orientation line DD in
the local horizontal plane with respect to a fixed reference line
RR (shown in FIG. 6 for improved clarity), such as true north. The
reference station 1111 also determines the vertical or polar angle
.theta..sub.v between the horizontal line DD and a separation
vector SV (of length d) that joins the reference station and the
mobile station 1131.
The reference station 1111 further includes an SATPS signal antenna
1121, which may form part of a handle or other structure for the
instrument 1111, that receives SATPS signals from two or more
satellites that are part of a Satellite Positioning System. The
SATPS signals received by the SATPS antenna 1121 are passed to an
SATPS receiver/processor 1123 that analyzes these signals and
determines the location of the antenna. The SATPS signal
receiver/processor 1123 (1) identifies the SATPS satellite source
for each SATPS signal, (2) determines the time at which each
identified SATPS signal arrives at the antenna, and (3) determines
the present location of the SATPS antenna from this information and
from information on the ephemerides for each identified SATPS
satellite. The SATPS signal antenna and signal receiver/processor
are part of the user segment of a particular SATPS, the Global
Positioning System, as discussed by Tom Logsdon in The NAVSTAR
Global Positioning System, Van Nostrand Reinhold, 1992, pp. 33-90,
incorporated by reference herein.
The reference station 11 also includes a first station
communication means, including a first transmitter, receiver or
transceiver 1124 and first communications antenna 1125, for
transmitting information to and/or receiving information from the
mobile station 1131, and a common data output port 1127.
The mobile station 1131 includes a fourth body 1133 that is mounted
on a tripod, prism pole or other stable structure (not shown) and
is rotatable about an approximately vertical third axis CC.
Normally, the axes AA and CC are each aligned to the local
gravitational force vector so that AA and CC are parallel to each
other only for very small separations between the reference station
1111 and the mobile station 1131. The fourth body 33 includes an
EDM responder 1135 that responds to incident electromagnetic waves,
such as W, and produces a return signal that is received and
understood by the EDM 1119. The EDM 1119 and the EDM responder 1135
work cooperatively to determine the distance or range from the
reference station 1111 to the mobile station 1131 and/or an angle
between the station separation vector SV and a selected reference
line, such as a true northline passing through the reference
station. The azimuthal angle (horizontal) and polar angle
(vertical) for the separation vector SV are determined using an
optical encoder that is included in the digital theodolite.
The mobile station 1131 also includes a second SATPS signal antenna
1137 and a second SATPS signal receiver/processor 1139, connected
together, that also receive SATPS signals from two or more SATPS
satellites and determine the location of the second SATPS antenna
from these SATPS signals. The mobile station 1131 may include a
common data output port 1138 for first or second station location
information.
The mobile station 1131 also includes a second transmitter,
receiver or transceiver 1140 and second communications antenna 1141
that allows communication between the reference station 1111 and
the mobile station 1131. In one mode of operation of the system
shown in FIG. 1, the reference station 1111 receives SATPS signals,
makes code phase and/or carrier phase measurements, compares the
location of the reference station indicated by these signals with
the location of the reference station that is known with high
accuracy from another source, and transmits location correction
information to the mobile station 1131. This information may
include the unprocessed code phase and/or carrier phase information
plus corrections to the SATPS-determined reference station
location, based upon the known reference station location.
The reference station 1111 determines the difference in three
location spatial coordinates and/or a local time coordinate and
transmits these coordinate differences to the mobile station, using
the first and second communications antennas 1125 and 1141. The
mobile station 1131 then uses the reference station measurements
and mobile station location information, plus the local SATPS
measurements, to accurately determine the location of the second
SATPS antenna 1137 relative to the location of the first SATPS
antenna 1121. Alternatively, in a second mode of operation, the
mobile station 1131 transmits its SATPS-determined location carrier
wave attribute or pseudorange attribute and/or time coordinates and
height of instrument and relevant status information (such as
meteorological data and remaining battery charge) to the reference
station 11, using the first and second communications antennas 1125
and 1141. The first SATPS receiver/processor 1123 receives these
coordinates and corrects the coordinates for the second SATPS
antenna 1137, using the measurements for the first SATPS antenna
1121.
In a third mode of operation, the reference station 1111 receives
SATPS data from a remote station (not shown in FIG. 11) whose
location is precisely known in a geodetic reference frame. The
reference station 1111 uses this information to precisely determine
its own location and the location of the mobile station 1131 in the
desired reference frame.
FIG. 12 illustrates one suitable EDM responder 1135 for the mobile
station 1131 in FIG. 11, an electromagnetic wave retro-reflector 51
that includes two highly reflective surfaces 1153a and 1153b that
are oriented perpendicularly to each other. Alternatively, the
retro-reflector 1151 may include an array of antenna components
1153a and 1153b that receives an incident electromagnetic wave at a
microwave or infrared frequency and produces a retro-directed wave
that proceeds away from the retro-reflector 1151 in the opposite
direction, as illustrated in U.S. Pat. No. 4,985,707, issued to
Schmidt and Kadim, incorporated by reference herein.
An incident electromagnetic wave W1 approaches the first
surface/array 53a at an arbitrary incidence angle .phi.1, is
reflected as a wave W2 that approaches the second surface/array
1153b, and is reflected by this second surface/array as a wave W3
at a reflectance angle .pi./2-.phi.1. The wave W3 thus moves away
from the retro-reflector 1151 in the same direction as, but
oppositely directed to, the direction of approach of the incident
wave W1. The incident wave W1 is thus returned toward the EDM 1119
in FIG. 1 as an anti-parallel wave W3. The EDM responder 35 in FIG.
11 may be an optical retro-reflector of well known design if the
incident electromagnetic wave W1 has a wavelength that lies in the
near-infrared, visible or ultraviolet range. If the incident wave
W1 has a far-infrared or microwave or longer wavelength, the EDM
responder 1135 may be an array of antenna elements for
retro-direction of the incident wave, as indicated above.
FIGS. 13A and 13B illustrate one embodiment of the system 1161 of
the reference station 1111 and of the system 1171 of the mobile
station 1131, respectively. The reference station system 1161
includes: (1) an SATPS measurement subsystem 1162 that receives
SATPS satellite signals and computes or otherwise determines or
computes the SATPS-determined location of the first SATPS antenna
1121 (FIG. 11); (2) a total station subsystem 1163 that includes
the EDM 1119 and provides horizontal and/or vertical distance
and/or angular displacement information and/or azimuthal
displacement information for the mobile station 1131 relative to
the reference station 1111; (3) a data link subsystem 1164 that
receives SATPS location information from and/or transmits SATPS
location information from the mobile station 1131; (4) a data
processing subsystem 1165 that receives information from the
subsystems 1162, 1163 and/or 1164 and provides information on the
location of the mobile station 31 relative to the reference station
1111; and (5) a user interface subsystem 1166 that receives
information from the data processing subsystem 1165 and displays
and stores this information in a useful format or formats for a
person performing survey activities at the reference station
1111.
The mobile station system 1171 shown in FIG. 3 includes: (1) an
SATPS measurement subsystem 1172 that receives SATPS satellite
signals, makes carrier phase and code phase measurements, and
determines the SATPS-determined location of the second SATPS
antenna 1137 (FIG. 1); (2) a data link subsystem 1173 that receives
SATPS location information from and/or transmits SATPS location
information from the reference station 1111; (3) a voice message
and/or data link 1174 (optional) that connects the reference
station data link subsystem 1164 with the mobile station data link
subsystem 1173 and allows the operators at the two stations to
communicate with each other; (4) a data processing subsystem 1175
that receives information from the subsystems 1172 and/or 1173
and/or 1176 and provides information on the location of the mobile
station 1131; and (5) a user interface subsystem 1176 that receives
information from the data processing subsystem 1175 and displays
and stores this information in a useful format or formats for a
person performing survey activities at the mobile station 1131.
The data link element 1173 shown in FIG. 3B may be implemented in
several ways. A first implementation introduces modulation into the
optical wave or radiowave W used for sighting of the mobile station
1131 from the reference station 1111 (FIG. 1). With reference to
FIG. 12, if the wave W1 is optical, the reflecting surfaces 1153a
and 1153b are provided with electrically sensitive backings 1155a
and 1155b, respectively, that sense these modulations on the
optical wave W1 and transfer these sensed modulation signals to a
signal demodulator 1157 that demodulates and determines the content
of these signals. Because the incident wave W1 and first reflected
wave W2 will be intercepted by the respective reflectors 1153a and
1153b, each of the two sensitive backing layers 1155a and 1155b
should sense substantially the same modulated signal; and either or
both of these sensed modulation signals can be used by the
demodulator 1157. As one alternative, the modulation signals sensed
by the sensitive backing layer 55b can be used as an error check
for the modulation signals sensed by the sensitive backing layer
1155a. If the wave W1 is a radiowave, the modulations introduced
into the wave W1 can be sensed by one or more of the antenna
elements in the retro-directing antenna array and, again,
demodulated by a signal demodulator.
A second implementation of the data link 1173 shown in FIG. 3B uses
a radio link established by the antennas 1125 and 1141 and
associated transmitters and receivers 1124 and 1140, as illustrated
in FIG. 11. This data link has the advantage that the link can
provide one-way or two-way communication between the reference
station 1111 and the mobile station 1131.
At least three approaches can be adopted for data receipt and
processing in the embodiment shown in FIGS. 13A and 13B. In a first
approach, the mobile station system 1171 receives the SATPS signals
(including satellite attributes information) through its SATPS
measurement subsystem 1172 and transmits these signals to the
reference station system 1161, where the SATPS-determined locations
of the reference station and of the mobile station are computed,
the reference station location correction (=known reference station
location-SATPS-determined reference station location) is computed,
and the SATPS-determined mobile station location is corrected using
the reference station location correction. In this approach, the
data processing subsystem 1175 and the user interface subsystem
1176 in the mobile station system 1171 are optional and can be
deleted.
In a second approach, the reference station system 1161 receives
the SATPS signals through its SATPS measurement subsystem 1162 and
transmits these signals to the mobile station system 1171, where
the SATPS-determined locations of the reference station and of the
mobile station are computed, the reference station location
correction is computed, and the SATPS-determined mobile station
location is corrected using the reference station location
correction. The known location of the reference station can be
transmitted from the reference station to the mobile station, or
this known location information can be stored in the SATPS
measurement subsystem 1172 or the data processing subsystem 1175 of
the mobile station system 1171. In this approach, the data
processing subsystem 1165 and the user interface subsystem 1166 in
the reference station system 1161 are optional and can be
deleted.
In a third approach, the mobile station system 1171 receives the
SATPS signals through its SATPS measurement subsystem 1172,
determines the mobile station location, and transmits the
SATPS-determined mobile station location information to the
reference station system 1161. .DELTA.t the reference station
system 1161, the SATPS-determined reference station location is
computed, the reference station location correction is computed,
and the SATPS-determined mobile station location is corrected using
the reference station location correction. In this approach, the
user interface subsystem 1176 in the mobile station system 1171 is
optional and can be deleted.
FIGS. 14A and 14B are front and back views, respectively, of a
representative conventional electronic total station 1181 from the
prior art. The front view in FIG. 4A illustrates a carrying handle
1183, instrument height mark 1185, electronic memory card and cover
1187, alphanumeric display 1189, clamps 1191 and 1193, circular
level 1195 with associated level adjusting screws 1197, level
adjusting foot screws 1199, Tribach 9101, horizontal circle
positioning ring 9103, keyboard 9105 for data and instruction
entries, an objective lens 9107 for survey line-of-sight
positioning, and a base plate 9109. The back view (operator side)
of the station 1181 in FIG. 14B illustrates a slot for a tubular
compass 9113 in the handle 1183, a battery or other power supply
9115, an optical plummet focusing ring 9117 and focusing eyepiece
9118, a power switch 9119, a horizontal clamp 120, a vertical clamp
121, a horizontal fine motion adjustment screw 9122, a data output
electronic connector 9123, an external power supply connector 9125,
a horizontal plate level 9127 and adjusting screw 9129, a vertical
fine motion adjustment screw 9131, a telescope transitting knob
9133, a telescope eyepiece 9135 (connected with the objective lens
9107 in FIG. 14A), a telescope focussing ring 9137, and a peep
sight 9139 for further viewing of a scene in which a survey
measurement will be made.
SATPS carrier phase measurements contain an integer phase ambiguity
that must be resolved to obtain centimeter-level accuracies on
station location. FIG. 15 illustrates two intersecting wavefront
sequences arising from carrier waves received from two SATPS
satellites, the actual location MS of a mobile station antenna
1137, and several adjacent other candidates MSC for the mobile
station location. An EDM and digital reading of vertical slope
between the reference and mobile stations provides valuable
information for resolution of these integer phase ambiguities. The
known distance d shown in FIG. 16 between the reference station
antenna 1121 and the mobile station antenna 1137 limits the integer
search region for the integer phase ambiguities to a sphere of
radius d. In practice the distance d will be known only within a
small uncertainty.+-..DELTA.d, and the search region becomes a
volume between two concentric spheres of radius d.+-..DELTA.d.
The search region is further reduced by applying the known height
difference d.sub.v between the two antennas 1121 and 1137, which is
determined from knowledge of the distance d and the vertical angle
.theta..sub.v relative to a horizontal line DD in FIG. 16. In
practice, the vertical angle .theta..sub.v will have a small
uncertainty.+-..DELTA..theta..sub.v associated with it. The search
can now be limited to an annular region defined by intersection of
the two concentric spheres of radius d.+-..DELTA.d and the region
between two cones having a common apex at the reference station
antenna 21 and apex angles equal to
.pi./2-(.theta..sub.v.+-..DELTA..theta..sub.v). An angular
displacement .theta..sub.h between a reference line RR and the line
DD can used to re-establish lost satellite lock.
The height difference between the reference and mobile stations
1111 and 1131 are related to the geoid, while the SATPS
measurements are related to a fixed ellipsoidal reference system.
Unless the coordinate differences between the geoid system and this
reference system have been determined beforehand, the antenna
height difference d.sub.v must also take account of the
uncertainties, if any, in the geoid-ellipsoid reference systems. As
long as the separation distance d is small (.ltoreq.10 km), the
geoid-ellipsoid height difference should be no more than a few
centimeters in reasonably flat terrain. The integer search region
might be approximated by an ellipsoid, as in FIG. 16, or by a
curvilinear parallelepiped, as in FIG. 17.
Further reduction in the integer search region may be realized by
taking advantage of the available differential SATPS code
measurements, which provide an unambiguous estimate of the mobile
station location relative to the reference station, with an
inaccuracy of no more than about five meters. The accuracy of the
code-based location solution governs the resulting size of the
integer search region, which is now reduced to a sector of the
ellipse of revolution, as illustrated in FIG. 16. Only those
carrier phase integer ambiguity combinations that fall within the
sector indicated in FIG. 16 are considered as candidates. The
integer combination with the smallest dispersion is preferably
chosen as the correct combination. If the correct integer
combination is not immediately apparent from a single measurement
epoch, additional satellite geometries over the course of time may
be used to average out errors and to further eliminate incorrect
integer combinations.
One of the first references to discuss ambiguity resolution
techniques in a GPS context is Counselman and Gourevitch,
"Miniature Interferometer Terminals for Earth Surveying: Ambiguity
and Multipath with Global Positioning System", I.E.E.E. Trans. on
Geoscience and Remote Sensing, vol. GE-19 (1981) pp.24414 252,
incorporated herein by reference. The published search algorithms
rely on a statistical measure of the quality of different ambiguity
integer combinations, in order to identify the correct ambiguities
for the tracked satellites.
Some computational efficiencies have been incorporated in integer
search algorithms disclosed by Hatch in U.S. Pat. Nos. 4,963,889
and 5,072,227, and by Euler and Landau in "Fast GPS Ambiguity
Resolutions On-the-fly for Real-time Applications", Sixth
International Geodetic Symposium on Satellite Positioning, Columbus
Ohio, Mar. 17-20 1992, incorporated by reference herein. Search
techniques for ambiguity integers have also been disclosed where
the distance between two SATPS receivers (e.g., at reference and
mobile stations) is known. The Hatch patents, U.S. Pat. No.
5,101,356, issued to Timothy et al, and U.S. Pat. No. 5,148,179,
issued to Allison, incorporated by reference herein, discuss other
techniques for resolution of integer ambiguities. The capability of
tightly constraining the integer ambiguity search based upon height
difference and separation distance of two SATPS antennas is
particularly valuable here. Thus, several techniques exist for
resolution of integer ambiguities, and such techniques can be
applied here in performing carrier-phase positioning in the context
of this invention.
An SATPS antenna, receiver/processor and other appropriate
equipment can be retrofitted to, and even integrated into the
housing for, the conventional electronic total station 1181 shown
in FIGS. 14A and 14B. For example, an SATPS antenna 1121 of
appropriate design and SATPS receiver/processor 1123 can be
incorporated in the top of the handle 1183 in FIG. 14A, as
suggested in FIG. 11. Alternatively, the SATPS receiver/processor
can be positioned in 1115 of FIG. 11 at any convenient place
therein. A second antenna 1125 and transceiver 1124 for the
reference station 1111 and a second antenna 1141 and transceiver
1140 for the mobile station 1131 can be positioned at any
convenient places on those stations, for communicating with each
other. Preferably, the SATPS components and related communications
components 1121, 1123, 1124 and 1125 on the reference station 1111
should share a common data port and a common power supply connector
with the other reference station components; and the SATPS
components and related communications components 1137, 1139, 1140
and 1141 for the mobile station 1131 should share a common data
port and a common power supply connector with the other mobile
station components.
A configuration of two or more receivers can be used to accurately
determine the relative positions between two stations. This method,
known as differential positioning, is far more accurate than
absolute positioning, provided that the distances between these
stations are substantially less than the distances from these
stations to the satellites, which is the usual case. Differential
positioning can be used for survey or construction work in the
field, providing location coordinates and distances that are
accurate to within a few centimeters.
In differential position determination, many of the errors in the
SATPS that compromise the accuracy of absolute position
determination are similar in magnitude for stations that are
physically close. The effect of these errors on the accuracy of
differential position determination is therefore substantially
reduced by a process of partial error cancellation.
This invention herein relies upon a combination of differential
satellite positioning system (DSATPS) and electro-optical distance
and angle measurements to provide highly accurate position
information on the location of one or more mobile stations relative
to a reference station whose location is known or determined with
high accuracy.
A Satellite Positioning System (SATPS) is a system of satellite
signal transmitters, with receivers located on the Earth's surface
or adjacent to the Earth's surface, that transmits information from
which an observer's present location and/or the time of observation
can be determined. Two operational systems, each of which qualifies
as an SATPS, are the Global Positioning System and the Global
Orbiting Navigational System.
The Global Positioning System (GPS) is part of a satellite-based
navigation system developed by the United States Defense Department
under its NAVSTAR satellite program. A fully operational GPS
includes up to 24 satellites approximately uniformly dispersed
around six circular orbits with four satellites each, the orbits
being inclined at an angle of 55.degree. relative to the equator
and being separated from each other by multiples of 60.degree.
longitude. The orbits have radii of 26,560 kilometers and are
approximately circular. The orbits are non-geosynchronous, with 0.5
sidereal day (11.967 hours) orbital time intervals, so that the
satellites move with time relative to the Earth below.
Theoretically, three or more GPS satellites will be visible from
most points on the Earth's surface, and visual access to two or
more such satellites can be used to determine an observer's
position anywhere on the Earth's surface, 24 hours per day. Each
satellite carries a cesium or rubidium atomic clock to provide
timing information for the signals transmitted by the satellites.
Internal clock correction is provided for each satellite clock.
Each GPS satellite transmits two spread spectrum, L-band carrier
signals: an L1 signal having a frequency f1=1575.42 MHz and an L2
signal having a frequency f2=1227.6 MHz. These two frequencies are
integral multiples f1=154 f0 and f2=120 f0, using a base frequency
f0=10.23 MHz. The L1 signal from each satellite is binary phase
shift key (BPSK) modulated by two pseudo-random noise (PRN) codes
in phase quadrature, designated as the C/A-code and P-code. The L2
signal from each satellite is BPSK modulated by only the P-code.
The nature of these PRN codes is described below.
One motivation for use of two carrier signals L1 and L2 is to allow
partial compensation for propagation delay of such a signal through
the ionosphere, which delay varies approximately as the inverse
square of signal frequency f (delay .varies.f.sup.-2). This
phenomenon is discussed by MacDoran in U.S. Pat. No. 4,463,357,
which discussion is incorporated by reference herein. When transit
time delay through the ionosphere is determined, a phase difference
associated with a given carrier signal can be determined.
Use of the PRN codes allows, use of a plurality of GPS satellite
signals for determining an observer's position and for providing
navigation information. A signal transmitted by a particular GPS
signal is selected by generating and matching, or correlating, the
PRN code for that particular satellite. All PRN codes are known and
are generated or stored in GPS satellite signal receivers carried
by ground observers. A first PRN code for each GPS satellite,
sometimes referred to as a precision code or P-code, is a
relatively long, fine-grained code having an associated clock or
chip rate of f0=10.23 MHz. A second PRN code for each GPS
satellite, sometimes referred to as a clear/acquisition code or
C/A-code, is intended to facilitate rapid satellite signal
acquisition and hand-over to the P-code and is a relatively short,
coarser-grained code having a clock or chip rate of f0/10=1.023
MHz. The C/A-code for any GPS satellite has a length of 1023 chips
or time increments before this code repeats. The full P-code has a
length of 259 days, with each satellite transmitting a unique
portion of the full P-code. The portion of P-code used for a given
GPS satellite has a length of precisely one week (7,000 days)
before this code portion repeats. Accepted methods for generating
the C/A-code and P-code are set forth in the document GPS Interface
Control Document ICD-GPS-200, published by Rockwell International
Corporation, Satellite Systems Division, Revision A, Sep. 26, 1984,
which is incorporated by reference herein.
The GPS satellite bit stream includes navigational information on
the ephemeris of the transmitting GPS satellite and an almanac for
all GPS satellites, with parameters providing corrections for
ionospheric signal propagation delays suitable for single frequency
receivers and for an offset time between satellite clock time and
true GPS time. The navigational information is transmitted at a
rate of 50 Baud. A useful discussion of the GPS and techniques for
obtaining position information from the satellite signals is found
in Tom Logsdon, The NAVSTAR Global Positioning System, Van Nostrand
Reinhold, N.Y., 1992, incorporated by reference herein.
A second configuration for global positioning is the Global
Orbiting Navigation Satellite System (GLONASS), placed in orbit by
the former Soviet Union and presumed to be maintained by the
Russian Republic. GLONASS also uses 24 satellites, distributed
approximately uniformly in three orbital planes of eight satellites
each. Each orbital plane has a nominal inclination of 64.8.degree.
relative to the equator, and the three orbital planes are separated
from each other by multiples of 120.degree.longitude. The GLONASS
circular orbits have smaller radii, about 25,510 kilometers, and a
satellite period of revolution of 8/17 of a sidereal day (11.26
hours). A GLONASS satellite and a GPS satellite will thus complete
17 and 16 revolutions, respectively, around the Earth every 8 days.
The GLONASS system uses two carrier signals L1 and L2 with
frequencies of f1=(1.602+9 k/16) GHz and f2=(1.246+7 k/16) GHz,
where k (=0, 1, 2, . . . , 23) is the channel or satellite number.
These frequencies lie in two bands at 1.597-1.617 GHz (L1)and
1,240-1,260 GHz (L2). The L1 code is modulated by a C/A-code (chip
rate=0.511 MHz) and by a P-code (chip rate=5.11 MHz). The L2 code
is presently modulated only by the P-code. The GLONASS satellites
also transmit navigational data at at rate of 50 Baud. Because the
channel frequencies are distinguishable from each other, the P-code
is the same, and the C/A-code is the same, for each satellite. The
methods for receiving and analyzing the GLONASS signals are similar
to the methods used for the GPS signals.
Reference to a Satellite Positioning System or SATPS herein refers
to a Global Positioning System, to a Global Orbiting Navigation
System, and to any other compatible satellite-based system that
provides information by which an observer's position and the time
of observation can be determined, all of which meet the
requirements of the present invention. A Satellite Positioning
System (SATPS), such as the Global Positioning System (GPS) or the
Global Orbiting Navigation Satellite System (GLONASS), uses
transmission of coded radio signals, with the structure described
above, from a plurality of Earth-orbiting satellites. A single
passive receiver of such signals is capable of determining receiver
absolute position in an Earth-centered, Earth-fixed coordinate
reference system utilized by the SATPS.
Preferably, the operation of optical unit 3 is automatic. That is,
optical unit 3 automatically locates optical target 34 and
determines the location of optical target 34. The calculations
performed correspond to well known surveying calculations performed
to determine the location of a target given the known location and
bearing of the measurement device and the latitude and departure of
the target from the measurement device. See e.g., Charles A.
Herubin, Principles of Surveying, (Prentice Hall, 1991) pp 8-15. In
one embodiment, a servo system (not shown) within optical unit 42
aligns theodolite 45 and EDM 44 with optical target 34 of FIG.
3.
FIG. 5A shows an embodiment of a SATPS base unit 1 adapted to
receive SATPS signals from satellites of the SATPS and retransmit
the received SATPS signals. SATPS system 52 includes SATPS antenna
53 that is adapted to receive signals from SATPS satellites. The
received signals are processed by SATPS receiver 54 and are coupled
to processor 55. Processor 55 controls the operation of SATPS base
unit 1. In one embodiment, SATPS base unit 1 continually receives
and retransmits signals received from SATPS satellites.
Alternatively, SATPS base unit 1 receives transmissions from rover
unit 2, and responds by transmitting signals received from SATPS
satellites.
Continuing with FIG. 5A, communication link 51 is used to couple
data between SATPS base unit 1 and rover unit 2. Communication link
51 includes radio transceiver 32 and radio antenna 33. Though rover
unit 2, optical unit 3, and SATPS base unit 1 of FIGS. 3-5A are
shown to include transceivers 32, alternatively, depending on the
desired configuration of the system, a transmitter, a receiver, or
a separate transmitter and receiver may be used.
In one embodiment, communication links 31, 41, and 51 of FIGS. 3-5A
couple data over an unlicensed frequency such as, for example 144
MHz or 900 MHz. Alternatively, other frequency bands could be used
for transmitting and receiving data. Alternatively, other methods
for coupling data between optical unit 3, SATPS base unit 1 and
rover unit 2 of FIGS. 1 and 3-5A may be used such as, for example
infrared transmission.
The individual components of optical unit 3 may be incorporated
into a single housing. Alternatively, one or all of the components
of optical unit 3 may be separate units connected together.
Similarly, the components of SATPS base unit 1 of FIG. 5A may be
incorporated into a single housing. Alternatively one or all of the
components of SATPS base unit 1 may be separate units that are
connected together. When separate units are connected together, a
communication port and corresponding cables are used, and
preferably, the communication port and cables conform to an
interface standard such as, for example, RS-232, RS-422, Ethernet,
CAN bus/ISO-11898/SAE-J1939, Mil-Std 1553, and the like.
In an alternate embodiment shown in FIG. 5B the functions of both
optical unit 3 of FIG. 4 and SATPS base system 1 of FIG. 5A are
incorporated into a single integrated unit that is shown as
integrated base unit 60. In this embodiment, communication link 61
transmits and receives both SATPS data and optical data. In one
embodiment, processor 65 controls the operations of SATPS system
52, optical system 42 and communication link 61. Input device 56 is
operable to input necessary data for operation of optical system 42
and to configure SATPS system 52.
Referring now back to FIG. 3, survey logic unit 36 determines the
optimum source of position data (step 22 of FIG. 2). When position
is to be determined using SATPS data, SATPS data is received via
communication link 31 and is coupled to SATPS processor 36 of SATPS
system 30. Signals from satellites of the SATPS are received by
SATPS antenna 39 and are coupled to SATPS receiver 40. SATPS
processor 36 determines position using the SATPS signals received
at SATPS antenna 39 and the signals from SATPS base unit 1.
At least three approaches can be used to determine position using
SATPS data. In one approach, SATPS base unit 1 is located at a
known location and SATPS data received by SATPS base unit 1 is
transmitted to rover unit 2 along with the position of SATPS base
unit 1. SATPS processor 36 uses the known location of SATPS base
unit 1 and the SATPS data received by SATPS base unit 1 to
determine the necessary corrections. SATPS processor 36 then
accurately determines location using the determined corrections and
signals from satellites of the SATPS received at SATPS antenna 39
and processed by SATPS receiver 40.
In a second approach, SATPS base unit 1 receives signals from
satellites of the SATPS and uses its known position to determine
the necessary corrections. These corrections are then transmitted
to rover unit 2 which uses the correction information, along with
signals received from satellites of the SATPS to accurately compute
its position.
In a third approach, signals received from satellites of the SATPS
are received at SATPS base unit 1 and are coupled directly to rover
unit 2. At rover unit 2, signals received from satellites of the
SATPS are used along with the signals received at base unit 1 to
determine position of rover unit 2 using carrier phase measurement
methods. Such methods are well known in the art and are commonly
used in RTK position determination. In one embodiment, an
appropriate algorithm that resolves integer phase ambiguity is used
to determine position with centimeter level accuracy. A useful
discussion of algorithms and methods for position determination
using multiple SATPS receivers is contained in U.S. Pat. No.
5,519,620 titled Centimeter Accurate Global Positioning System
Receiver for On-The-Fly Real-Time Kinematic Measurement and Control
which is incorporated herein by reference. Another useful reference
that is incorporated herein as background material is Jay Van
Sickle, GPS for Land Surveyors (Ann Arbor Press, Inc. 1996) pp.
33-110.
In one embodiment, the SATPS of FIGS. 3-5B uses satellites of the
GPS to determine position. In this embodiment, SATPS systems 52 is
a standard GPS system as are commonly used in RTK positioning
systems for determining position. That is, SATPS antenna 53 is a
standard GPS antenna and SATPS receiver is a standard GPS receiver
adapted to receive signals from satellites of the GPS. In this
embodiment, SATPS system 30 of FIG. 3 is a standard GPS system,
with SATPS antenna 39, SATPS receiver 40 and SATPS processor 36
adapted to determine position using satellites of the GPS and
signals coupled from other GPS systems.
When position is to be determined using optical data, information
is coupled to survey logic unit 36 from a source of optical data
such as optical unit 3 of FIGS. 1 and 4. In one embodiment, the
received information includes a determination of position that is
calculated by optical unit 3. Alternatively, position is calculated
by processor 37 using information coupled from optical unit 3. When
position is calculated by processor 37, the information transmitted
from optical unit 3 includes ranging information(i.e. the distance
and direction from optical unit 3 to rover unit 2) and the position
of optical unit 3. In one embodiment, the position of optical unit
3 (FIG. 4) and the alignment of optical unit 3 are coupled to
processor 37 (FIG. 3) along with the angles measured by theodolite
45 and the distance measured by EDM 44.
Referring back to FIG. 2, once position is determined using the
optimum source of position information, as shown by steps 20-23,
the position is coupled to the user. In one embodiment, the
position is displayed on a display device such as display device 31
of FIG. 3. Display device 31 is a liquid crystal display or other
suitable display mechanism. Alternatively, or in conjunction with
the display of the determined position on display device 31, the
position is stored for later analysis (post-processing) in data
storage device 38. In one embodiment, data storage device 38 is a
Dynamic Random Access (DRAM), a Static Random Access Memory (SRAM),
or a flash memory device.
In one embodiment, processors 37, 55 and 65 of FIGS. 3-5B are
general-purpose microprocessors such as Motorola 68000
microprocessors. Alternatively, processors 37, 55 and 65 are an
ASIC device or a FPGA device.
In one embodiment of the present invention, the seamless surveying
system of the present invention is implemented in a computer such
as computer 600 shown in FIG. 6. That is, the operations of survey
logic unit 36 and/or display device 31 and input device 35 are
performed by computer 600. It is appreciated that the computer 600
of FIG. 6 is exemplary only and that the present invention can
operate within a number of different computer systems other than
the computer system illustrated in FIG. 6. Other computing systems
include general purpose computer systems, embedded computer
systems, and stand alone computer systems specially adapted for use
in the present invention.
Computer 600 of FIG. 6 includes an address/data bus 612 for
communicating information, a central processor unit 614 coupled to
bus 612 for processing information and instructions, Signal input
and output communications device 628 of computer 600 is coupled to
bus 612. In one embodiment, signal input and output communications
device 628 includes a radio demodulator for demodulating radio
signals which may be directly coupled from one or more antennas to
input output communications device 628. Alternatively, radio
signals may be received, demodulated and transmitted in digital
form to input and output through communications device 628.
Computer 600 also includes data storage features such as random
access memory 616 coupled to bus 612 for storing information and
instructions for central processor unit 614, read only memory 618
coupled to bus 612 for storing static information and instructions
for the central processor unit 614, and data storage device 620
(e.g., a magnetic or optical disk and disk drive) coupled to bus
612 for storing information and instructions. Computer 600 also
includes display device 622 which is coupled to bus 612 for
displaying information (e.g., a map showing the position of the
rover unit and/or the surveyed site, previously surveyed sites and
data points, etc.) to an operator. Computer 600 may also include an
output communications port for transmitting the position to
external devices--either other computers or other user interfaces.
An alphanumeric input device 624 including alphanumeric and
function keys is coupled to bus 612 for communicating information
and command selections to central processor unit 614. Computer 600
also includes cursor control device 626 that is coupled to bus 612
for communicating user input information and command selections to
central processor unit 614.
Display device 622 of FIG. 6, utilized with computer 600 of the
present invention is a liquid crystal device, cathode ray tube, or
other display device suitable for creating graphic images and/or
alphanumeric characters recognizable to the user. Referring now to
FIG. 6, cursor control device 626 allows the computer user to
dynamically signal the two dimensional movement of a visible symbol
(cursor) on a display screen of display device 622. Many
implementations of cursor control device 626 are known in the art
including a trackball, mouse, touch pad, joystick or special keys
on alphanumeric input device 624 capable of signaling movement of a
given direction or manner of displacement. Alternatively, it will
be appreciated that a cursor can be directed and/or activated via
input from alphanumeric input device 624 using special keys and key
sequence commands. The present invention is also well suited to
directing a cursor by other means such as, for example, voice
commands.
With reference next to FIG. 7, a flow chart illustrating an
alternate method for determining the optimum source of position
data is shown. Upon initiating a position fix (step 601), a
specified amount of time is allowed to pass as shown by block 701.
The waiting period may be set, or may be user configurable. The
waiting period is sufficient for communication to be received from
both a SATPS base unit and an optical unit. In one embodiment, a
time of 5 seconds is used. However, depending on the particular
equipment being used, it may be desirable to increase or decrease
the waiting period to optimize performance.
If, within the predetermined amount of time, SATPS data is not
received as shown by decision block 702, and if optical data is not
received as shown by decision block 703, accurate determination of
the position of the rover unit is not possible. In that event, an
indication that insufficient data is available to determine
position will be given to the operator of the rover unit as shown
by block 705. This indication may be conveyed to the operator of
the rover unit by an indicator such as a light emitting diode, or
by the display of text, or by use of voice messaging.
Continuing with FIG. 7, if only optical data is received (step
703), then optical data is used to determine position (step 708).
If only SATPS data is received, as shown by steps 702 and 704,
SATPS data is the optimum source of position data as shown by step
707.
Still referring to FIG. 7, when both SATPS data and optical data
are received during the predetermined amount of time, a switch over
threshold (hereinafter "optical threshold") is used to determine
the best source of position data. That is, an optical threshold is
determined such that optical position data give an accurate
position fix when the distance between the optical unit and the
rover is less than the optical threshold. In effect, the optical
threshold determines the range within which optical position data
is to be used. In one embodiment, the threshold is set at 100
meters. Alternatively, the threshold may be user-defined so as to
allow the user to select a threshold that meets the user's specific
needs.
Still referring to FIG. 7, as shown by block 706, if both optical
data and SATPS data are available, and if the separation distance
between the rover and the base station is less than the optical
threshold distance, then the optical data is designated as the
optimum source of position data as shown by block 708. When both
optical data and SATPS data are available from a rover that is at a
distance greater than the optical threshold distance, SATPS data is
designated as the optimum source of position data as shown by block
707.
In another embodiment that is shown in FIG. 8, the determination of
the best source of position data is driven by the desired
precision. That is, the user determines the desired precision such
as, for example, two to three centimeters. This precision setting
is used for determining the best source of position data. First,
the desired precision threshold is established as shown by step
801. In one embodiment, the desired precision is set at two
centimeters.
Continuing with FIG. 8, position data is received as shown by step
800. In one embodiment, a rover unit such as rover unit 2 of FIGS.
1 and 3 is used.
Still referring to FIG. 8, each type of incoming position data is
analyzed to determine the precision of the determination of
position that would be obtained using the incoming position data as
shown by step 802. This process may be performed using any of a
number of known methods. In one embodiment, the signal to noise
ratio of incoming SATPS data is used. Alternatively, other factors
such as the number of SATPS satellites received or the geometry of
the received satellites is used in determining the precision. When
the incoming data is optical data, the signal strength and/or the
distance between the optical unit and the rover is used to
determine the precision of the determination of position.
The determination of precision for each received source of position
data is then compared to the precision threshold as shown by step
803. If the precision for a source of position data is greater than
or equal to the precision threshold, that source of position data
is selected as the optimum source of position data as shown by step
804. Otherwise, as shown by arrow 805, the process continues until
such time that an incoming source of position data meets the
established precision threshold. Thus, the first source of position
data that gives a position within the desired accuracy range is
designated as the optimum source of position data.
Referring now to FIG. 9, in one embodiment, weighting factors are
applied so as to weight optical position data and SATPS position
data separately. In one embodiment, separation distance and signal
strength are used to weight each incoming optical data source.
Continuing with FIG. 9, the number of satellites received by the
rover unit, distance between the rover unit and the base unit
(separation distance), and RTK correction data accuracy are taken
into account in weighing SATPS data. In one embodiment, RTK
correction data accuracy is determined using the number of
satellites received at the base unit, cycle slips, and measurement
quality. Cycle slips are a function of the number of continuously
locked measurements of correction data broadcast by the base
station. Measurement quality is a statistical estimator of the
inherent uncertainty of the measurement process. Measurement
quality can take many forms, including standard deviation of the
actual measurements, Root Mean Square (RMS), Circular Error
Probability (CEP), Carrier/Noise Ratio (C/No), or some other Figure
of Merit for relative comparison of different measurement
sources.
Referring still to FIG. 9, the weighting factors for each variable
are multiplied with the respective variable and the total for both
optical data and SATPS data is summed. Whichever data source has
the highest total is used as the optimum data source.
FIG. 10 shows yet another embodiment of the present invention. As
shown by steps 601, 701-703 and 705, if no position data is
received after a predetermined amount of time, an indication that
insufficient data is available is given. If only one source of
position data is available, that source of position data is
designated as the optimum source of position data. More
specifically, as shown by steps 701-703, when optical data is the
only source of position data, optical data is designated as the
optimum source of position data (step 101) and is used to determine
position (step 102). Similarly, as shown by steps 701, 702 and 704,
when SATPS data is the only source of position data, SATPS data is
designated as the optimum source of position data (step 103) and is
used to determine position (step 104).
Continuing with FIG. 10, when both optical data and SATPS data are
received, both optical data and SATPS data are used to determine
position and the results are averaged to determine position as
shown by step 105.
The foregoing descriptions of specific embodiments of the present
invention have been presented for purposes of illustration and
description. They are not intended to be exhaustive or to limit the
invention to the precise forms disclosed, and obviously many
modifications and variations are possible in light of the above
teaching. The embodiments were chosen and described in order to
best explain the principles of the invention and its practical
application, to thereby enable others skilled in the art to best
utilize the invention and various embodiments with various
modifications as are suited to the particular use contemplated. It
is intended that the scope of the invention be defined by the
Claims appended hereto and their equivalents.
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